(a) Field of Invention
The invention relates generally to hearing protection devices and, more particularly to a method of forming an earplug by laser ablation.
(b) Description of Related Art
The use of hearing protective and noise attenuating devices is well known, and various types of devices are available including, but not limited to, ear muffs, semi-aural devices, and earplugs. Earplugs are often preferred for their effectiveness in attenuating sound and for comfort properties provided thereby.
An earplug generally comprises a sound attenuating element which is placed in the ear canal of a wearer to provide desired sound attenuation. The sound attenuating element is commonly made of a compressible, resilient material such as a foam or a rubber.
There are many instances in which it is desirable to produce the sound attenuating element having a cavity formed therein or a channel formed therethrough or, more generally, with a certain quantity of the compressible, resilient material removed or otherwise made absent from a body of the sound attenuating element.
For example, a cavity formed in the sound attenuating element of an earplug may be used to receive an end of a cord element which is bonded to the sound attenuating element in the cavity and used to connect two earplugs together. Herein, the term “cavity” will be used to designate a hole or recess formed in the sound attenuating element of an earplug but not completely through the sound attenuating element.
Such a cavity may be used in another embodiment to receive and mount therein a rigid or semi-rigid stem used to provide a degree of rigidity to the earplug and to effect convenient insertion and removal thereof. Still further, such a cavity may be formed in an earplug to receive a detectable material such as a metal, magnetic or x-ray identifiable substance for providing easy detectability of the earplug. Still further, a cavity may be formed within the sound attenuating element so that the earplug exerts less pressure on a wearer's ear canal upon insertion thereof, thus providing greater comfort to the wearer.
A channel formed through the sound attenuating element of an earplug may be used to facilitate communication with the wearer of the earplug. Herein, the term “channel” will be used to designate a hole or recess formed in a sound attenuating element of an earplug which propagates completely through the sound attenuating element such that the channel is open to an exterior of the earplug in at least two places.
Such a channel may be used to facilitate communication by, for example, receiving a communications insert, such as a receiver, transducer, etc., designed to deliver sound to a wearer. Alternatively, the channel may receive a tube for connection to a communication assembly which delivers sounds through the tube, into the ear canal of the wearer.
In another example, a certain quantity of the compressible, resilient material used to compose the sound attenuating element of an earplug may be desired to be removed or otherwise made absent from an outer surface of the element in order to form surface ornamentation, such as indicia or patterning, thereon. Such indicia includes characters and logos while the patterning includes surface elements for visual styling, gripping, etc.
The items discussed above (the cavity, channel, surface ornamentation) and other similar features may be formed in the earplug sound attenuating element either during production or shortly after production thereof.
For example, where the sound attenuating element is formed in a molding process, such as an injection molding process, the mold may include features which form the items, in situ, during molding. For example, the mold may include an insert about which the sound attenuating element is formed. Removal of the insert after formation of the compressible, resilient material results in the desired cavity or channel. The mold may include other elements which function similarly to the insert in order to form the surface ornamentation, i.e., indicia, patterning, etc.
However, such a molding technique often results in inconsistent formation of the described items. That is, it has been found that the sizing and placement of the cavity, the channel, etc. formed through in situ molding techniques often varies from one earplug to the next. Such inconsistent results are clearly not desirable. In addition, an earplug manufacturer would require several different earplug molds in order to produce sound attenuating elements having cavities, channels, and/or surface ornamentation, thus, increasing costs and generally complicating manufacturing.
The sound attenuating element of an earplug may also be formed through a casting process in which the resilient, compressible material, is formed in a sheet and then later die cut into pieces to form sound attenuating elements. Formation of the cavity, channel, or surface ornamentation during this casting process is not possible. Such features must be formed after casting of the sound attenuating elements by mechanical means, etc. However, this involves additional manufacturing and processing steps and, additionally, the features produced are often inconsistent from one attenuating element to the next or are otherwise inadequate.
Extrusion processes are often used to form the compressible, resilient sound attenuating elements for earplugs. However, such processes do not allow for creation of cavities or channels in the sound attenuating elements during formation thereof. Thus, in the case of extruded sound attenuating elements, as well as with preformed molded sound attenuating elements, features such as cavities, channels, or surface ornamentation must be formed in the sound attenuating element in a separate manufacturing step conducted after the initial formation of the sound attenuating element.
For example, after formation of a sound attenuating element, the cavity, channel, etc., may be effectively cut into the compressible, resilient material. Particularly, a high speed drill may be used to bore the cavity or channel into the sound attenuating element. However, this technique is insufficient because the drill tends to rip or tear the compressible, resilient material. Also, the rotating drill may pull the sound attenuating element from its fixture during drilling, thus interrupting manufacturing. In another technique, a thermal element having a high temperature is pressed into the sound attenuating element to effectively melt the compressible, resilient material in order to form the cavity, channel, etc. However, this method also results in inconsistent formation of the cavity, channel, etc. Specifically, a diameter of the cavity and channel varies considerably over manufacture of a number of earplugs, at least partly due to a build up of burnt compressible, resilient material adhering to the thermal element.
As mentioned, a sound attenuating element of an earplug may be formed to include a cavity for receiving a rigid or semi-rigid stem used to provide a degree of rigidity to the earplug and to effect convenient insertion and removal thereof. In one embodiment, the stem includes a stem cavity formed at one end of the stem for receiving an end of a cord element therein. The cord element is attached to the stem in the stem cavity and attached at an opposite end to a second stem of a second earplug, thus forming a corded pair of stemmed earplugs.
The stem may be formed, for example, by an extrusion process. During such process it is not possible to form the stem cavity. The stem cavity must be formed in a separate manufacturing process, for example, by boring a hole into the stem with a drill after extrusion formation of the stem. Alternatively, the stem may be produced through a molding or a casting process in which the stem cavity is created, respectively, in situ during formation of the stem or afterwards via a mechanical process. In either case, formation of the stem cavity by traditional methods often results in inconsistent placement of the cavity within the stem and inaccurate cavity dimensions.
Thus, a method of removing material from an earplug to effectively, efficiently, and consistently form surface elements in the earplug's sound attenuating element or stem, such as a cavity, a through-channel, and surface ornamentation, is desired.